Method for the production of etched foils for use in the construction of slot nozzles for the separation of isotopes

ABSTRACT

A method for the production of etched foils for use in sandwich construction of slot nozzle assemblies used in separating isotopes wherein a copper-beryllium foil which is coated on two sides with a photo lacquer, is masked on both sides in such a manner as to leave a narrow unmasked gap outlining the area to be etched from the foil, exposing the masked foil on both sides to collimated light, developing the exposed photo lacquer layer, removing the exposed photo lacquer layer and whirling an etching solution over the foil to etch away the areas of the foil underlying the exposed photo lacquer.

United States Patent 1191 Konstantouros et al.

[ METHOD FOR THE PRODUCTION OF ETCHED FOILS FOR use IN THE CONSTRUCTION OF SLOT NOZZLES FOR THE SEPARATION OF ISOTOPES [75] Inventors: Efthimios Konstantouros; Juergen Michel; Ruprecht Von Siemens, all of Munich; Karl Stoll, Neusaess, all of Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin & Munich, Germany [22] Filed: Mar. 19, 1971 [21] Appl. No.: 126,175

[30] Foreign Application Priority Data Apr. 21, 1970 Germany 2019201 [52] U.S. Cl 96/36, 156/18, 252/792 [51] Int. Cl G03c 5/00 [58] Field of Search 96/36, 36.2; 156/18, 345; 252/792 [56] References Cited UNITED STATES PATENTS 3,443,915 5/1969 Wood et a1. 96/362 UX 3,556,957 1/1971 Toledo et al 252/792 X 3,156,563 11/1964 Harrison et al. 96/36 1451 Apr. 30, 1974 3,356,023 12/1967 Schuttenberg 96/364 x 1,081,290 12/1913 Albert 156/345 x OTHER PUBLICATIONS Photoetching Forms Thin Parts, Steel, Vol. 141, No. 2, Nov. 1957, pp. 153-156.

Damon; G. Exposing Sources for Kodak Resists, Kodak Photoresist, Seminar Proceedings, 1968 Ed., Vol. 11, p. 20 only.

Primary Examiner-David Klein Attorney, Agent, or Firm-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT A method for the production of etched foils for use in sandwich construction of slot nozzle assemblies used in separating isotopes wherein a copper-beryllium foil which is coated on two sides with a photo lacquer, is masked on both sides in such a manner as to leave a narrow unmasked gap outlining the area to be etched from the foil, exposing the masked foil on both sides to collimated light, developing the exposed photo lacquer layer, removing the exposed photo lacquer layer and whirling an etching solution over the foil to etch away the areas of the foil underlying the exposed photo lacquer.

3 Claims, 3 Drawing Figures METHOD FOR THE PRODUCTION OF ETCHED FOILS FOR USE IN THE CONSTRUCTION OF SLOT NOZZLES FOR THE SEPARATION OF ISOTOPES BACKGROUND OF THE INVENTION Physical separation of isotopes of an element to provide for instance a material of isotopic composition different from that which occurs in nature can be performed through several different processes. Such a process may be particularly important in a number of fields such as the nuclear energy field sine individual isotopes may have completely different nuclear properties. In recent times it has been proposed that isotopes can be separated by allowing a gaseous compound to pass through a properly shaped nozzle which may be referred to as a slot nozzle. Such slot nozzle arrangements and their use in practice is for instance described in the essay entitled Entmischung der Uranisotope in Einer Zehnstufigen Treenduesenversuchsanlage [Separation of Uranium Isotopes in a Ten Stage separating Nozzle testing Device] by E. W. Becker, G. Frey, R. Schuette and D. Seidel in the magazine Atom Wirtschaft [Atom Economy] of July 1968, pp. 359 through 362. In such slot nozzle separation devices gas is passed through a supply channel and the gaseous isotope mixture which is guided through the gas supply and is speeded up to supersonic speed by passing the isotope mixture through a so-called Lavall nozzle against a deflection wall. The heavier isotopes adhere to the deflection wall and the lighter ones tend to separate slightly from it and a so-called peeler is interposed in the path of these separated isotopes to pass them respectively to heavy and light isotope carry-off channels.

In order to effectively perform this operation, rather long slot nozzle sections are required and such long slot nozzles with the extremely fine tolerances required, can heretofore only be produced with the greatest difficulty. 7

As noted in copending application Ser. No. 1 13,173, filed on Feb. 8, 1971, a slot nozzle assembly having the desired elongated slot nozzles formed therein can be manufactured by sandwiching together a plurality of thin metal foils having identical precisely formed openings therein corresponding to the cross-sectional configuration of the desired elongated slot nozzle. Such foils can be superposed one upon the other with the cross-sectionally configurated slot nozzles therein lying congruently with one another to define, in combination, an elongated slot nozzle. Several foils can then be bonded together to form the desired slot nozzle assembly. The end product of course may have a large'number of slot nozzles formed within it and is made up of a series of stacked foils.

Since the dimension of several of the openings and isotope paths inthe slot nozzle are extremely minute (microscopic) the formation of such foils is extremely critical.

The present invention relates to a method of producing such foils wherein outline etching of the desired openings in the foils is used. The etching method herein disclosed pennits the formation of foil openings having gaps with width on the order of nineteen microns with an allowed deviation of size of two microns.

It is therefore an object of the present invention to provide a method for producing foils for use in the sandwich construction of slot nozzle assemblies wherein the foils are masked on both sides in such a manner as to expose only a portion of the foils outlining the openings to be formed in the foils and subsequently exposing the masked foils to collimated light and thereafter removing the exposed photo lacquer on the foils by immersing the foils in an etching solution.

It is a further object of the invention to provide means for etching wherein the etching solution is air swirled within its container over the foils.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the present invention will become apparent from time to time as the following specification proceeds and with reference to the accompanying drawings, wherein:

FIG. 1 illustrates an individual foil with etched openings formed therein corresponding to the desired crosssectional configuration of a slot nozzle;

FIG. 2 is an enlarged representation of one of the slot nozzle cross sections of FIG. 1; and

FIG. 3 is a still further enlarged fragmentary view of a portion of the slot nozzle showing the Lavall nozzle, the deflector wall, and peeler.

Referring initially to FIG. 1 a foil is shown which is preferably formed of a copper-beryllium alloy and which has a series of openings formed therein corresponding to the desired cross-sectional configuration of an elongated slot nozzle. On the particular foil illustrated in FIG. 1 thirty-four nozzle cross sections are illustrated but it will be understood that in practice several hundred nozzle cross sections may be provided in a single foil. The copper-beryllium alloy foil preferably has a thickness on the order of about 15 microns and the openings therein provided are formed in a manner which will hereafter be described.

FIGS. 2 and 3 illustrate in greater detail the particular design of a slot nozzle wherein it may be seen how critical are the particular design and dimensioning of the openings and walls defining such openings.

The slot opening comprises three separate channels which may be said to consist of three separate lobes. The channel 10 comprises the gas supply channel wherein an isotope mixture is passed into the device. The large center lobe 11 comprises a light isotope carry-off channel and left hand lobe 12 comprises the heavy isotope carry-off channel.

In operation the slot nozzle assembly created by the stacked foils functions substantially as follows: A gaseous isotope mixture is passed down the supply channel 10 and the light and heavy isotopes are passed through the Lavall nozzle 13 and against the deflection wall 14 and .then tend to separate from one another. The heavier isotopes cling to the deflection wall while the lighter isotopes tend to separate from it. A sharp-edged peeler 15 is interposed in the path of the isotopes passing from the deflection wall 14 and this peeler acts to direct the heavier isotopes clinging to the deflection wall 14 into the heavy isotope carry off channel 12 and to direct the lighter isotopes into the channel 11.

As heretofore mentioned, details of the operation of this form of nozzle can be had by reference to the publication already above referred to.

For illustrative purposes it may be understood that a desired slot nozzle assembly may have gas supply and heavy isotope carry-off channels having a dimension on the order of 2.6 mm. The guiding metal lip 16 providing the converging wall of the nozzle will have a bending radius of 60 microns. The deflection wall has a radius of curvature of 100 microns and the rounding edge of the peeler has a radius of 4 microns.

The slot nozzle assembly is formed by placing a number of foils such as the foil illustrated in FIG. 1 in superposed relation with respect to one another with the opening formed within such foils in exact correspondence with one another. The resulting stack of foils is then preferably welded together although they may otherwise be bonded by means of gluing or soldering or the like.

The method of producing the identically configured stacked foils is substantially as follows. The foils themselves are formed from a roller hardened copperberyllium alloy with 1.7 percent beryllium content and a foil thickness of approximately 15 microns. The foils are cut to the desired general form and are then cleaned in several cleaning steps while applying suitable solvents as well as by immersing the foils in a hydrochloric acid solution. Such cleaning processes insure that no foreign particles remain on the foils. After the cleaning process a photo lacquer is applied to both surfaces of the foil and this photo lacquer is then permitted to dry resulting in a lacquer coating about microns thick on both sides of the foil.

Identical glass photo masks are then placed on both sides of the foil. The operator then views the masks under a microscope and adjusts the masks into absolute congruity with one another with the help of a mask adjusting device while the foil which is to be exposed lies between the two masks.

After the masks are thus adjusted, both sides of the foils are exposed to collimated light applied normal to the surface of the foil. The source of such collimated light may preferably be a high pressure mercury lamp.

After such exposure, the photo lacquer is developed in a well known manner and the photo lacquer previously exposed to the light is baked out, thus exposing the surface of the foil itself.

The resultant foil is then fixed into a plastic frame and is immersed into an etching solution which preferably consists of about 0.05 through 0.l5 m.p.l. CrO 0.0 through 0.15 m.p.l. H 80 and 0.07 through 0.6 m.p.l. HCl. During the immersion process the etching bath is also preferably whirled within its container over the foil by means of pressurized air so that an even etching of even the finest portions of the nozzle openings is assured. The etching time will last about seventy seconds. Toward the end of the etching process, the foils are quickly removed from the bath and post etched once or twice after having been examined microscopically. After the etching process is finished photo lacquer is then removed by placing the foil in an acetone bath and ultrasonically vibrating the bath.

The etching is preferably effected in accordance with the outline etching principle wherein the glass photo masks are designed to cover all portions of the underlying foil except for a small narrow area outlining the portions to be removed. Hence, the major portions of the lobes of the slot nozzle would themselves also be covered by the photo masks and only the outline of those lobes would be exposed to the collimated light. With this process only a very narrow gap is etched and this gap should be as wide as the widest place in the main structure, that is, about 40 microns. in order to obtain the desired optimum gap width between the parts 14 and 19 microns, the separation channel in the mask should have a width of 8 through 10 microns. With such a mask-gap width, the required gap width is obtained when the foils being etched have a thickness of about 15 microns.

What I claim is:

l. A method of producing copper-beryllium alloy foils for use in the construction of slot nozzle assemblies for the separation of isotopes wherein a series of foils are stacked in sandwich form to define the slot nozzle assembly comprising the steps of cleaning a thin metal foil of copper-beryllium,

coating both sides of the foil with a photo lacquer,

placing symmetrical light masks on each side of the foil and in complete congruity with one another with the masks masking all portions of the foil to be exposed to light but for a narrow gap outlining each of the areas to be etched from the foil,

exposing both sides of the masked foil to collimated light applied to the foil,

developing the exposed photo lacquer layer and removing such exposed layers, and

exposing the resulting foil to an etching solution consisting of 0.05 through 0.15 mol/ 1 CrO 0.0 through 0.15 mol/ 111 50 and 0.7 through 0.6 mol/ ll-lCl to etch away the areas of the foil underlying the exposed photo lacquer.

2. A method for the production of foils for use in the construction of slot nozzle assemblies for the separation of isotopes as defined by claim 1, comprising the additional step of whirling the etching solution over the foil by air during the etching process.

3. The method of producing foils for use in the construction of slot nozzle assemblies for the separation of isotopes in accordance with claim 2, including the additional steps of placing the foil in an acetone bath and ultrasonically vibrating the bath to effect removal of the remaining photo lacquer. 

2. A method for the production of foils for use in the construction of slot nozzle assemblies for the separation of isotopes as defined by claim 1, comprising the additional step of whirling the etching solution over the foil by air during the etching process.
 3. The method of producing foils for use in the construction of slot nozzle assemblies for the separation of isotopes in accordance with claim 2, including the additional steps of placing the foil in an acetone bath and ultrasonically vibrating the bath to effect removal of the remaining photo lacquer. 